Specific heat of twisted bilayer graphene: Engineering phonons by atomic plane rotations

Nika, Denis L.; Cocemasov, Alexandr I.; Balandin, Alexander A.

doi:10.1063/1.4890622

Cited by 75 publications

(87 citation statements)

References 53 publications

(80 reference statements)

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“…In addition to a numerical solution we also provide a simple analytical formula for calculating c v (T) for graphene, BLG and T-BLG with parameters extracted from the Born-von Karman model of the lattice vibrations. We have earlier proposed a possibility of engineering phonon dispersion and materials properties by twisting of the atomic planes in T-BLG [23][24]. The first experimental studies of heat conduction in suspended T-BLG confirmed that twisting substantially reduces K owing to the increased scattering phase space available for phonons in T-BLG as compared to the Bernal-stacked BLG [25].…”

Section: Introductionmentioning

confidence: 87%

Engineering of the thermodynamic properties of bilayer graphene by atomic plane rotations: the role of the out-of-plane phonons

2015

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We investigated theoretically the specific heat of graphene, bilayer graphene and twisted bilayer graphene taking into account the exact phonon dispersion and density of states for each polarization branch. It is shown that contrary to a conventional belief the dispersion of the out-of-plane acoustic phonons - referred to as ZA phonons - deviates strongly from a parabolic law starting from the frequencies as low as ∼100 cm(-1). This leads to the frequency-dependent ZA phonon density of states and the breakdown of the linear dependence of the specific heat on temperature T. We established that ZA phonons determine the specific heat for T ≤ 200 K while contributions from both in-plane and out-of-plane acoustic phonons are dominant for 200 K ≤ T ≤ 500 K. In the high-temperature limit, T > 1000 K, the optical and acoustic phonons contribute approximately equally to the specific heat. The Debye temperature for graphene and twisted bilayer graphene was calculated to be around ∼1861-1864 K. Our results suggest that the thermodynamic properties of materials such as bilayer graphene can be controlled at the atomic scale by rotation of the sp(2)-carbon planes.

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Section: Introductionmentioning

confidence: 87%

Engineering of the thermodynamic properties of bilayer graphene by atomic plane rotations: the role of the out-of-plane phonons

2015

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“…It has been shown that phonon energies strongly depend on the interatomic force constants (IFCs)-fitting parameters of interatomic interactions, used in the majority of the models. Therefore a proper choice of interatomic force constants is crucial for the accurate description of phonon energy spectra and thermal conductivity in graphene, twisted graphene and graphene nanoribbons [1][2][3]44,86].…”

Section: Theory Of the Thermal Conductivity Of Graphene And Gnrmentioning

confidence: 99%

Graphene Thermal Properties: Applications in Thermal Management and Energy Storage

2014

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Abstract:We review the thermal properties of graphene, few-layer graphene and graphene nanoribbons, and discuss practical applications of graphene in thermal management and energy storage. The first part of the review describes the state-of-the-art in the graphene thermal field focusing on recently reported experimental and theoretical data for heat conduction in graphene and graphene nanoribbons. The effects of the sample size, shape, quality, strain distribution, isotope composition, and point-defect concentration are included in the summary. The second part of the review outlines thermal properties of graphene-enhanced phase change materials used in energy storage. It is shown that the use of liquid-phase-exfoliated graphene as filler material in phase change materials is promising for thermal management of high-power-density battery parks. The reported experimental and modeling results indicate that graphene has the potential to outperform metal nanoparticles, carbon nanotubes, and other carbon allotropes as filler in thermal management materials. OPEN ACCESSAppl. Sci. 2014, 4 526

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“…We employ the density functional tight-binding (DFTB) method 15 to describe graphene while the van der Waals (vdW) interaction between the sheet and the substrate is modelled with the 6-12 Lennard-Jones (LJ) potential V LJ ðrÞ ¼ 4 LJ ððr=rÞ 12 À ðr=rÞ 6 Þ. 16,29 The direction transverse to the step (y) is described by periodic boundary conditions using 8 k y -points in the DFTB force-constant calculations. The ends of the sheet are first left free to float at a fixed distance over the substrate, in order to find the correct bending geometry.…”

Section: 14mentioning

confidence: 99%

Phonon scattering in graphene over substrate steps

Sevinçli

Brandbyge

2014

Applied Physics Letters

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We calculate the effect on phonon transport of substrate-induced bends in graphene. We consider bending induced by an abrupt kink in the substrate, and provide results for different step-heights and substrate interaction strengths. We find that individual substrate steps reduce thermal conductance in the range between 5% and 47%. We also consider the transmission across linear kinks formed by adsorption of atomic hydrogen at the bends and find that individual kinks suppress thermal conduction substantially, especially at high temperatures. Our analysis show that substrate irregularities can be detrimental for thermal conduction even for small step heights. V C 2014 AIP Publishing LLC.[http://dx.doi.org/10.1063/1.4898066]Graphene is the material with the highest thermal conductivity reported so far, 1-3 with important prospective applications for example for thermal management of nanoelectronics. 4,5 The ultimately thin membrane adhere well to substrates and typically will ripples, wrinkles, and bubbles form when graphene is transferred onto a flat substrate. On the other hand, since graphene is known to cling to the smallest irregularities, 6 this also results in deformation and bending caused by the conformation of graphene to a irregular surface. This could, for instance, be steps in surfaces such as SiC or edges of other 2D materials such as BN. It is thus highly relevant to consider the effects of deformation on the thermal transport properties of graphene. There are several recent studies which investigate the effects of substrate induced geometrical modulations on the electronic and transport properties of graphene. [7][8][9][10] In particular, Low and coworkers 9 considered the effect on the electronic transport when graphene is deformed due to physisorption on a flat substrate presenting an abrupt step. They used a simple Lennard-Jones potential to model the substrate-graphene interaction with parameters corresponding to a step in SiC, and found that the bend itself causes an insignificant scattering of the electrons. Also, the related effect of ripples and wrinkles on electronic structure and transport in graphene on substrates has been investigated. 11-13Inspired by the study of Low et al., 9 we here consider phonon transport for a model of an abrupt step in a otherwise structureless substrate. We calculate the transport for various step-heights and interaction strengths. The effects of the substrate are two-fold. First, (i) the geometry of graphene is modulated by the irregularity of the substrate, which alters the force constants locally and therefore scatters phonons. Second, (ii) the substrate gives rise to a renormalization of the vibrational modes and increases the line widths (i.e., reduces phonon lifetimes). Here, we focus on the deformation (i) and neglect the dynamics of the structureless substrate.We find that the effect of the substrate induced bend in the graphene on the phonon transport is not negligible, and can reduce the conductance with more than 10% at room temperature. For very stro...

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Specific heat of twisted bilayer graphene: Engineering phonons by atomic plane rotations

Cited by 75 publications

References 53 publications

Engineering of the thermodynamic properties of bilayer graphene by atomic plane rotations: the role of the out-of-plane phonons

Engineering of the thermodynamic properties of bilayer graphene by atomic plane rotations: the role of the out-of-plane phonons

Graphene Thermal Properties: Applications in Thermal Management and Energy Storage

Phonon scattering in graphene over substrate steps

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